1. Field of the Invention
The present invention is in the field of chemical synthesis and is directed to a method for the preparation of bromonitro-alcohols.
2. Description of the Prior Art
As discussed in U.S. Pat. No. 3,658,921, issued to Wessendorf, the preparation of aliphatic bromonitro-alcohols is generally carried out in one of the following manners. The alkaline earth salt (generally sodium or calcium) of the desired nitro-alcohol is prepared from a nitro-alkane and an aldehyde with strong aqueous caustic or a metal alcoholate in alcoholic solution. By one process, the nitro-alcohol (or its metal salt) in solution is then reacted with bromine in an organic solvent such as ether, chloroform, or carbon tetrachloride. Alternatively, the salt is isolated and brominated as a suspension in an organic solvent, or is reacted with bromine in an aqueous solution by use of a phase transfer catalyst.
Several drawbacks and disadvantages are inherent in these approaches. The methods require the use of organic solvents which are either flammable, toxic, or both, and are dangerous when used in commercial scales. Isolation of the salts of the nitro-alcohols, involving the filtration and purification of said salts, is very time consuming, even in small batches. Also, the sodium salts of the nitro-alcohols are not very stable, and when exposed to air, decomposition begins even after a short time. Any heating or a slight blow can lead to a spontaneous decomposition, which may be vigorous, or even violent. An alternate approach would involve bromination of the nitro-alkane prior to the aldol reaction. However, it is indicated in the Wessendorf patent that unsatisfactory results are obtained when bromination of the nitroparaffin is attempted prior to the reaction with the aldehyde, especially when the nitroparaffin used is nitromethane. Wessendorf states that the reaction between bromonitromethane and an aldehyde gives an unsatisfactory result, that result being a low yield.
The preparation of bromonitro-alcohols according to the Wessendorf Patent 3,658,921 occurs as follows. A nitro-alkane is reacted with an aldehyde and an inorganic salt of a member of the group consisting of magnesium and alkaline earth metals in an aqueous medium to form the magnesium or alkaline earth metal salt of the nitro-alcohol. This nitro-alcohol salt is then brominated without isolation in an aqueous suspension at a temperature below 25.degree. C.
An alternate process for preparing bromonitro-alcohols is described in U.S. Pat. No. 3,711,561, issued to Wessendorf, et al. The process of U.S. Pat. No. 3,711,561 comprises reacting a nitro-alkane with an aldehyde in an alkaline metal hydroxide in the presence of water to obtain an aqueous solution of the alkaline metal salt of the nitro-alcohol, and reacting the aqueous solution with bromine at a temperature less than 25.degree. C. Both Wessendorf patents disclose procedures involving the isolation of the salts of the nitro-alcohols, which causes great difficulties. As indicated, the difficulties include the time-consuming filtration and purification of such salts, as well as the high instability of the salts.
In the late 1800's, M. L. Henry described the reaction of aldehydes and nitroparaffins, catalyzed by solid bases. Louis Henry, "Nitrated Alcohols", Recueil Travaux Chim Pays Bas Belgique 16, 250-252 (1897); Louis Henry, "Research on Mono-Carbonated Derivatives", Bull. Acad. Roy. Belgique 29 (Sec. 3), 834-842 (1895). His procedure entailed the admixing of the subject nitroparaffin in a solution of the aldehyde, and adding an amount of a solid base. When his experiments were duplicated in our laboratory, it was demonstrated that the method he described is undesirable for large scales due to the suddenness and intensity of the exothermic reaction. The purity of the product obtained by his method is also less than desirable.
In the Japanese Patent Application No. 1987-[Showa 62]-290,580, filed Nov. 17, 1987 (disclosed on May 25, 1989 as No. 1989-[Hei 1]-132,549), Hirahato, et al. reacted bromonitromethane with a strongly alkaline solution of formaldehyde. A consequence of their procedure is that the strongly alkaline aqueous solution of the product must be treated with sulfuric acid to prevent decomposition of the product in the alkaline medium. A result of making the solution alkaline, and its subsequent acidification, is the introduction of additional water to a system that contains a water-soluble product. Upon processing the reaction mixture by removing the water, the isolated product is contaminated by undesirable inorganic sulfate salts which are insoluble in the organic residue. A further disadvantage of this process results from the addition of the alkaline solution of this reagent aldehyde to the substrate bromonitromethane. This addition order places the halogenated nitro-alkane in a stoichiometric excess in the immediate reaction zone, a situation which favors incomplete reaction, with the concurrent formation of undesirable and hard-to-handle lachrymatory liquid monohydroxyalkylated by-products, and lowering of yields.
The preparation of halogenated nitro-alcohols is described in U.S. Pat. No. 4,922,030, issued to Nocito, et al. as follows. A halonitro-alkane is reacted with a substantially nonaqueous solution of an aldehyde, in the presence of an alkaline catalyst, to form the halonitro-alcohol. The alcohol is subsequently recovered from the reaction mixture. The Nocito, et al. patent is limited to a process involving an organic solvent and occurring at an alkaline pH.
A process for producing dibromonitro compounds is also disclosed in U.S. Pat. No. 4,723,044, which issued Feb. 2, 1988 to M. Watanabe et al. The reaction disclosed therein comprises condensing nitromethane with formaldehyde or acetaldehyde in the presence of alkali. The amount of alkali is at least 1.5 moles per mole of nitromethane. Thereafter, without isolating the product, the reaction mixture is treated with bromine, and the dibromonitro compound is recovered. See also the European Patent Application No. 0 364 789 Al, published Apr. 25, 1990.